1. Field of the Invention
The present invention relates to a zoom lens suitable for an imaging apparatus equipped with a solid state image sensor such as a charge-coupled device (CCD) and a complementary metal-oxide-semiconductor (CMOS).
2. Description of the Related Art
An abundance of zoom lenses have been proposed that can be mounted to an imaging apparatus equipped with a solid state image sensor such as a CCD and a CMOS. Recently, rapid advances in achieving high pixel counts of solid state image sensors have enabled finer features of a subject to be seen and many zoom lenses for megapixel counts have emerged (for example, refer to Japanese Patent Laid-Open Publication Nos. 2011-154390 and 2006-3589).
In addition to advances in achieving high pixel counts, there is a rising need for high resolution zoom lenses having a long focal length and capable of handling megapixel counts under the visible light range to the near-infrared light range to enable reliable high-image recording for the collection of evidence by a surveillance camera during a crime as well as during normal times. Further, consequent to strong demand for reductions in the size of imaging apparatuses, a zoom lens that is simple and compact is desirable.
Although the zoom lens recited in Japanese Patent Laid-Open Publication No. 2011-154390 realizes a high zoom ratio lens having a simple structure, with respect to near-infrared light, axial chromatic aberration and chromatic difference of magnification at the telephoto edge is prominent and optical performance markedly deteriorates. Further, with the zoom lens recited in Japanese Patent Laid-Open Publication No. 2006-3589, although aberration at high zoom ratios and up to the near-infrared light range is corrected, the light output from a third group has a tendency to diverge and therefore, aberration variations consequent to focusing become large and high optical performance cannot be maintained. Furthermore, differences in optical performance arise among manufactured products.